Production method of liquid crystal display including scanning exposure

ABSTRACT

To provide: a production method of a liquid crystal display device, the production method being capable of efficiently and stably providing alignment treatment for an alignment film of the liquid crystal display device, in which a plurality of domains is formed in a pixel region; and an exposure device for alignment treatment. A production method of a liquid crystal display device comprising: a first substrate; a second substrate facing to the first substrate; a liquid crystal layer provided between the substrates; a first alignment film provided on the liquid crystal layer side surface of the first substrate; and a second alignment film provided on the liquid crystal layer side surface of the second substrate, wherein the production method comprises subjecting the first alignment film and/or the second alignment film to scanning exposure continuously over a plurality of pixel regions, and the scanning exposure comprises exposing the first alignment film and/or the second alignment film while scanning an inside of each pixel region more than one time in antiparallel directions to form, in the each pixel region, regions for aligning liquid crystal molecules to the surface (s) of the first alignment film and/or the second alignment film in antiparallel directions.

This application is a continuation of U.S. patent application Ser. No.13/078,267 filed Apr. 1, 2011 now U.S. Pat. No. 8,064,019, which is acontinuation of Ser. No. 12/084,377 filed Apr. 30, 2008 now U.S. Pat.No. 8,130,348, which is the U.S. national phase of InternationalApplication No. PCT/JP2006/323045 filed 13Nov. 2006 which designated theU.S. and claims priority to Japanese Patent Application No. 2005-350020filed 2Dec. 2005, the entire contents of each of which are herebyincorporated by reference.

TECHNICAL FIELD

The present invention relates to a production method of a liquid crystaldisplay device and an exposure device for alignment treatment. Morespecifically, the present invention relates to a production method of amatrix-type liquid crystal display device which can provide high displayquality by forming a plurality of domains in one pixel region. Thepresent invention also relates to an exposure device for alignmenttreatment.

BACKGROUND ART

Liquid crystal display devices in TN (Twist Nematic) mode havewell-balanced characteristics needed for display devices. For example,the devices have a low driving voltage and a relatively fast responsespeed, and are suitably used for color display because the devicesprovide monochrome display in principle. Therefore, such liquid crystaldisplay devices in TN mode have been widely used for matrix-type liquidcrystal display devices such as an active matrix-type liquid crystaldisplay device and a simple matrix-type liquid crystal display device.However, such devices in TN mode also have disadvantages, such as anarrow viewing angel and a low contrast ratio.

Liquid crystal display devices in VA (Vertical Alignment) mode, whichhas a high contrast ratio, have been recently developed. In VA mode,liquid crystal molecules align substantially vertically to substrateswhen no voltage is applied between the substrates, and on the otherhand, the liquid crystal molecules align substantially parallel to thesubstrates when a voltage sufficiently greater than the thresholdvoltage is applied between the substrates. Domain division techniques ofdividing alignment directions of liquid crystal molecules in one pixelregion have been developed. These techniques enable one pixel region tohave a plurality of regions where the alignment directions of the liquidcrystal molecules are different (hereinafter, also referred to as“domain”). As a result, the liquid crystal display devices can provide awider viewing angle.

In addition, the following liquid crystal display devices in VA mode inwhich domain division is provided have been practically used. Liquidcrystal display devices in MVA (Multi-Domain Vertical Alignment) mode inwhich, as an alignment control structure, one substrate is provided withelectrode slits and the other substrate is provided with projectivestructures to perform the domain division; and liquid crystal displaydevices in PVA (Patterned Vertical Alignment) mode in which, as analignment control structure, both substrates are provided with electrodeslits to perform the domain division. These modes can provide liquidcrystal display devices having a high contrast ratio, which is anadvantage in VA mode, and a wide viewing angle, which is an advantage inthe domain division.

However, the liquid crystal display devices in MVA and PVA modes haveroom for improvement in slow response speed. That is, only liquidcrystal molecules near the electrode slits and the projective structuresfast start to respond, even if a high voltage is applied to change blackstate to white state, and liquid crystal molecules, which are far fromthe alignment control structures, respond late.

For improvement in this response speed, it is effective that alignmenttreatment is provided for alignment films formed on the liquid crystallayer side surfaces of substrates, whereby to provide liquid crystalmolecules with a pretilt angle previously. Also in VA mode, the liquidcrystal molecules are previously made slightly incline toward thevertical alignment films, and thereby the liquid crystal molecules caneasily incline when a voltage is applied to the liquid crystal layer. Asa result, the response speed can be faster. As a method of the alignmenttreatment for providing the liquid crystal molecules with the pretiltangle, rubbing method, SiOx oblique deposition method, andphoto-alignment method may be mentioned, for example.

The domain division is performed to obtain a wide viewing angle in MVAmode and PVA mode. However, there is room for improvement in that thenumber of the alignment treatment process for the alignment filmsincreases if the domain division is performed. In the photo-alignmentmethod, a domain division method of performing exposure through aphotomask more than one time has been proposed, for example. It ispreferable in terms of simplification of the production processes thatthe alignment treatment is performed with a small number of times.However, one pixel region has preferably two or more domains, and mostpreferably four or more domains in order to secure a wide viewing angle.Therefore, a method which can secure many domains with a small number ofalignment treatments has been desired.

As the VA mode in which domain division is provided, a VA mode usingvertical alignment films in which alignment directions on each other'ssubstrates are antiparallel in any domain, as shown in FIGS. 8 (a) and 8(b), (hereinafter, also referred to as VAECB (Vertical AlignmentElectrically Controlled Birefringence) mode) has been proposed. In VAECBmode, as shown in FIG. 8 (a), the direction of the absorption axis offirst polarizer 35 formed on the first substrate side and the directionof the absorption axis of second polarizer 36 formed on the secondsubstrate side are out of alignment with the alignment direction 31 a ofthe first alignment film 31 and the alignment direction 32 b of thesecond alignment film 32 by 45 degrees. In a mode of dividing one pixelregion into four domains, which is particularly excellent in viewingangle (hereinafter, also referred to as 4VAECB mode) in VAECB mode,throughput in volume production decreases since the alignment treatmentis performed in four directions, i.e. 45, 135, 225, and 315 degrees whenthe horizontal direction (azimuthal angle) on the display surface isdefined as 0 degree, as shown in FIG. 8 (b). For example, Japanese KokaiPublication No. 2001-281669 discloses a technique of performingalignment treatment by a photo-alignment method and thereby providingthe VAECB mode. However, in this case, the exposure is performed for thealignment films a total of eight times.

In contrast, VAHAN (Vertical Alignment Hybrid-aligned Nematic) mode, inwhich one substrate is provided with a vertical alignment film subjectedto no alignment treatment, can decrease the number of the alignmenttreatment. However, there is room for improvement in the response speedsince the pretilt angle of the liquid crystal molecules remains 90degrees on the other substrate side.

With this problem, a VAmode using vertical alignment films in whichalignment treatment directions on each other's substrates areperpendicular to cause liquid crystal molecules to form a twiststructure (hereinafter, also referred to as VATN

(Vertical Alignment Twisted Nematic) mode) has been proposed (forexample, with reference to Japanese Kokai Publication No. Hei-11-352486,Japanese Kokai Publication No. 2002-277877, Japanese Kokai PublicationNo. Hei-11-133429, and Japanese Kokai Publication No. Hei-10-123576). Ina liquid crystal display device in VATN mode, as shown in FIG. 5 (a),the first alignment film 31 and the second alignment film 32 align theliquid crystal molecules 33 with negative dielectric anisotropysubstantially vertically to the alignment film surfaces, and align theliquid crystal molecules 33 near the first alignment film 31 and theliquid crystal molecules 33 near the second alignment film 32 such thatthe alignment directions of them are perpendicular to each other, whenno voltage is applied between the substrates interposing the liquidcrystal layer (at OFF-state). Each of the liquid crystal molecules 33near the surfaces of the first alignment film 31 and the secondalignment film 32 has the pretilt angle 34 to the alignment films. Asshown in FIG. 5 (b), the liquid crystal molecules 33 align in thedirection parallel to the substrate surfaces as a voltage is appliedbetween the substrates interposing the liquid crystal layer, dependingon the applied voltage, and show birefringence to light transmittedthrough the liquid crystal layer. In VATN mode, as shown in FIG. 6 (a),the direction of the absorption axis of first polarizer 35 and thealignment direction 31 a of the first alignment film 31 are the same,and the direction of the absorption axis of second polarizer 36 and thealignment direction 32 b of the second alignment film 32 are the same.Alternatively, as shown in FIG. 6 (b), the direction of the absorptionaxis of first polarizer 35 and the alignment direction 32 b of thesecond alignment film 32 may be the same, and the direction of theabsorption axis of second polarizer 36 and the alignment direction 31 aof the first alignment film 31 may be the same. As shown in FIG. 7, amode of dividing one pixel region into four domains in VATN mode(hereinafter, also referred to 4VATN mode) needs only four times of thealignment treatment, which is half the number of times in 4VAECB mode.Such VATN mode is theoretically dramatically excellent in that a wideviewing angle and a fast response speed can be provided with a smallnumber of processes. However, a technique of producing the liquidcrystal display device in VATN mode has not been established yet.Additionally, the liquid crystal display device in VATN mode isdifficult to produce stably because variation in the pretilt angle has alarge influence on the transmittance as compared with the liquid crystaldisplay device in VAECB mode.

In a production process of a liquid crystal display panel, a panelsubstrate to be used becomes larger year by year in order to improveproduction efficiency and the like. With the enlargement of thesubstrate size, a large photomask has been needed in the photo-alignmentmethod which performs the exposure through a photomask. However, use ofthe large photomask has room for improvement in that distortion and thelike is generated in the photomask and thereby accuracy of the exposureis reduced.

A photomask having high-definition openings is extremely expensive, andtherefore, there is room for improvement in that use of the largephotomask increases manufacturing costs. With this problem, a method ofmoving a light source or a substrate (hereinafter, also referred to as“scanning exposure”) has been proposed as an exposure method (forexample, with reference to Japanese Kokai Publication No. Hei-09-211465,and Japanese Kokai Publication No. Hei-11-316379).

However, there is still room for improvement in that domains havingsmall variation in the characteristics are formed with a small number ofalignment treatments if domain division is performed by aphoto-alignment method.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, the present inventionprovides a production method of a liquid crystal display device, theproduction method being capable of efficiently and stably providingalignment treatment for an alignment film of the liquid crystal displaydevice, in which a plurality of domains is formed in a pixel region.

The present inventors have made various investigations about aproduction method of a liquid crystal display device, the productionmethod being capable of efficiently and stably providing alignmenttreatment for an alignment film of the liquid crystal display device, inwhich a plurality of domains is formed in a pixel region. The inventorsnoted an exposure method in a photo-alignment method. The inventorsfound that the alignment film is subjected to scanning exposurecontinuously over a plurality of pixel regions, which allows for morestable alignment treatment than that in simultaneous exposure in which alight source and a region to be exposed are fixed to expose the insideof the region to be exposed at one time. If a plurality of domains isformed inside a pixel region, the alignment film generally has acomplicated alignment pattern in the substrate plane. Therefore, in thescanning exposure, the number of times of the alignment treatmentdramatically increases or the alignment treatment itself is difficult.However, the inventors found that in VATN mode and the like, thealignment pattern continues in the substrate plane, and therefore, eachpixel region is exposed while scanning the each pixel region more thanone time in antiparallel directions to perform the alignment treatmentstably with a small number of alignment treatments. As a result, theabove-mentioned problems have been solved, leading to completion of thepresent invention.

That is, the present invention provides a production method of a liquidcrystal display device comprising:

a first substrate;

a second substrate facing to the first substrate;

a liquid crystal layer provided between the substrates;

a first alignment film provided on the liquid crystal layer side surfaceof the first substrate; and

a second alignment film provided on the liquid crystal layer sidesurface of the second substrate,

wherein the production method comprises subjecting the first alignmentfilm and/or the second alignment film to scanning exposure continuouslyover a plurality of pixel regions, and

the scanning exposure comprises exposing the first alignment film and/orthe second alignment film while scanning an inside of each pixel regionmore than one time in antiparallel directions to form, in the each pixelregion, regions for aligning liquid crystal molecules to the surface (s)of the first alignment film and/or the second alignment film inantiparallel directions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a plane view schematically showing a light beam emittingdirection to a photo-alignment film on a TFT array substrate inEmbodiment 1.

FIG. 1( b) is a plane view schematically showing a light beam emittingdirection to a photo-alignment film on a CF substrate in Embodiment 1.

FIG. 2( a) is a plane view schematically showing the TFT array substratethat is a first substrate in Embodiment 1.

FIG. 2( b) is a plane view schematically showing the CF substrate thatis a second substrate in Embodiment 1.

FIG. 3 is a perspective view schematically showing an exposure device inEmbodiment 1.

FIG. 4 is a perspective view schematically showing an exposure device inEmbodiment 2.

FIGS. 5( a) and 5(b) are conceptual views explaining drive principle ofa liquid crystal display device in VATN mode. FIG. 5( a) showsOFF-state, and FIG. 5( b) shows ON-state. Each of FIGS. 6( a) and 6(b)is a conceptual view showing positional relationships of alignmentdirections of alignment films and directions of absorption axes ofpolarizers in one domain of a liquid crystal display device in VATNmode. FIGS. 6( a) and 6(b) each show one embodiment of the positionalrelationships.

FIG. 7 is a conceptual view showing relationships of four domains andalignment directions of alignment films in one pixel of a liquid crystaldisplay device in 4VATN mode.

FIG. 8( a) is a conceptual view showing relationships of alignmentdirections of alignment films and directions of absorption axes ofpolarizers in one domain of a liquid crystal display device in VAECBmode.

FIG. 8( b) is a conceptual view showing relationships of four domainsand alignment directions of alignment films in one pixel of a liquidcrystal display device in 4VAECB mode.

BRIEF DESCRIPTION OF THE DRAWINGS

11: TFT

12: Pixel electrode

13: Black matrix (BM)

14: Color filter

15: Scanning signal line

16: Data signal line

17: BM above scanning line

18: BM above data line

20 a, 20 b: Exposure device

21: Stage

22: Light source

23, 23 a, 23 b: Photomask

24 a, 24 b: Opening

25: Camera for image detection

26: Substrate

31: First alignment film

32: Second alignment film

31 a: Alignment direction of the first alignment film 31

32 b: Alignment direction of the second alignment film 32

33: Liquid crystal molecule

34: Pretilt angle

35: Absorption axis of first polarizer

36: Absorption axis of second polarizer

A, B, C, D: Region

W1, W2: Width of opening

+x, −x, +y, −y: Scanning direction

DETAILED DESCRIPTION OF THE INVENTION

The present invention will, hereinafter, be described in more detail.

In the production method of the liquid crystal display device accordingto the present invention, the first alignment film and/or the secondalignment film are/is subjected to scanning exposure continuously over aplurality of pixel regions. The first alignment film and/or the secondalignment film are/is provided with alignment treatment (the alignmentdirections are defined) by the scanning exposure. More specifically, thefirst alignment film and/or the second alignment film are/is generallyphoto-alignment film(s) made of a material, in which the alignmentregulating force varies by photoirradiation and the alignment directionvaries depending on a photoirradiation direction or a moving directionof a photo-irradiated region. The “alignment direction” means adirection shown by projecting a tilt direction of the liquid crystalmolecule in the liquid crystal layer on to the substrate surface.

In the present invention, the scanning exposure is not especiallylimited as long as the exposure is performed while moving a position tobe irradiated with a light beam on the substrate surface. Specificembodiments of the scanning exposure include: an embodiment, in whichthe substrate surface is irradiated with a light beam emitted from alight source while moving the light source; an embodiment, in which thesubstrate surface is irradiated with a light beam emitted from a lightsource while moving the substrate; and an embodiment, in which thesubstrate surface is irradiated with a light beam emitted from a lightsource while moving the light source and the substrate. The scanningexposure can effectively suppress variation in characteristics of thealignment film, such as alignment direction and pretilt angle, becauseit is excellent in stability, such as stability in irradiance level inthe substrate plane, as compared with the simultaneous exposure. Inaddition, the scanning exposure uses a light source smaller than that inthe simultaneous exposure and the like, and thereby the exposure devicecan be smaller.

It is preferable that the above-mentioned scanning exposure controls thescanning direction while scanning a pattern on the substrate with acamera for image detection, and the like. Thereby, high-accuracyscanning exposure can be performed along a pixel array, even if thesubstrate is distorted. The pattern on the substrate, which is used forthe scanning, is not especially limited, but the pattern is preferablyprovided periodically or continuously along the scanning direction. Awiring, a black matrix and the like formed on the substrate can be used.

In the present invention, the scanning exposure comprises exposing thefirst alignment film and/or the second alignment film while scanning aninside of each pixel region more than one time (scanning to and from theinside of each pixel region at least one time) in antiparalleldirections to form, in the each pixel region, regions for aligningliquid crystal molecules to the surface (s) of the first alignment filmand/or the second alignment film in antiparallel directions. The regionexposed at the first exposure inside the pixel region and the regionexposed at the second exposure inside the pixel region may overlap, butthey are preferably substantially different. In the present description,“scanning in antiparallel directions” means that the movement directionsin the scanning are opposed to each other, and the courses in thescanning are parallel to each other. And “to form, in the each pixelregion, regions for aligning liquid crystal molecules to the surface (s)of the first alignment film and/or the second alignment film inantiparallel directions” means that a region P which aligns liquidcrystal molecules near the first alignment film and/or the secondalignment film in a direction and a region Q which aligns the liquidcrystal molecules near the first alignment film and/or the secondalignment films in a direction antiparallel to the alignment directionin the region P are formed in an inside of each pixel region. Therefore,the alignment direction in the region P and the alignment direction inthe region Q are out of alignment by substantially 180 degrees. Thealignment directions in the regions P and Q need not be strictly out ofalignment by 180 degrees, and may be substantially opposed. As describedabove, the scanning exposure is performed for the alignment film byscanning the pixel region in the direction A and the direction B that isthe reverse direction of the direction A and parallel to the directionA, whereby to easily perform alignment treatment of the liquid crystaldisplay device having two or more domains in one pixel. In the presentinvention, the scanning exposure is continuously performed over aplurality of pixel regions. Therefore, the alignment patternsantiparallel to each other continue over a plurality of pixel regionssubjected to the scanning exposure, in the alignment film of the liquidcrystal display device produced by the production method of the presentinvention. Therefore, the present invention is most preferably appliedas a production method of liquid crystal display devices in VATN modeand the like.

Examples of embodiments of the above-mentioned scanning exposureinclude: an embodiment, in which a spot light beam is emitted with aspot light source; an embodiment, in which a line light beam is emittedalong a scanning direction of the scanning exposure with a line lightsource; and an embodiment, in which exposure is performed through aphotomask with various light sources. In these embodiments, one pixelregion can be provided with an irradiated region and a non-irradiatedregion, which allows for domain division in which the alignmentdirections are antiparellel. Among these embodiments, the embodiment ofperforming exposure through a photomask can easily control the shape ofthe light beam by providing the photomask with desired openings,regardless of the shape of the light source. The present inventionadopts the scanning exposure. Therefore, even if an alignment filmformed on a large substrate is subjected to the alignment treatment, nolarge photomask is needed and therefore problems such as reduction inexposure uniformity caused by distortion of the photomask do not occur.

The “spot light beam” means a light beam having a spot shape on theirradiated substrate surface. For example, a laser light beam, a lightbeam in which light from the light source is condensed with an opticallens so as to have a spot shape, and the like, may be used. The “linelight beam” means a light beam having a substantially linear shape(strip-shaped) on the irradiated substrate surface. For example, a lightbeam in which light from the light source is condensed with an opticallens so as to have a substantially linear shape, and the like, may beused.

In the above-mentioned scanning exposure, the light beam is preferablymade incident from an oblique direction to the normal line on thesubstrate surface, although depending on the material of the alignmentfilm to be exposed. The incident angle of the light beam to the normalline on the substrate surface is preferably 5 degrees or more and 70degrees or less in VATN mode. This configuration can provide the liquidcrystal layer with a pretilt angle suitable in VATN mode. If theincident angle is less than 5 degrees, the pretilt angle is too small,resulting in significant decrease in response speed of the liquidcrystal display device. If the incident angle is more than 70 degrees,the pretilt angle is too large, and thereby a contrast ratio of theliquid crystal display device may be insufficient. However, the lightbeam does not need to have an incident angle, and the incident angle maybe 0 degree, if appearance of the pretilt angle depends on the movingdirection of the photo-irradiated region, as in the photo-alignmentmethod disclosed in “Photo-Rubbing Method: A Single-Exposure Method toStable Liquid-Crystal Pretilt Angle on Photo-Alignment Film”, M. Kimura,three et al, IDW′ 04: proceedings of the 11th International DisplayWorkshops, IDW′ 04 Publication committee, 2004, and LCT2-1, p. 35-38.

Various conditions in the scanning exposure, such as kind of lightsource, light exposure, size of light beam on the alignment filmsurface, scanning speed, and existence of polarizer, may beappropriately determined depending on conditions for forming thealignment film, such as desired alignment direction and pretilt angle.The “pretilt angle” means an angle formed by the alignment film surfaceand the longitudinal direction of the liquid crystal molecule near thealignment film when no voltage is applied to the liquid crystal layer(at OFF-state).

In the production method of the liquid crystal display device accordingto the present invention, processes other than the above-mentionedscanning exposure process are not especially limited as long as theproduction method of the present invention essentially includes theabove-mentioned scanning exposure process.

The liquid crystal display device produced by the production method ofthe present invention, comprises a first substrate, a second substratefacing the above-mentioned first substrate, a liquid crystal layerprovided between the above-mentioned substrates, a first alignment filmprovided on the liquid crystal layer side surface of the above-mentionedfirst substrate, and a second alignment film provided on the liquidcrystal layer side surface of the above-mentioned second substrate. Inthe configuration of the liquid crystal display device produced by thepresent invention, components are not especially limited as long as theliquid crystal display device essentially comprises standard componentsof matrix-type liquid crystal display devices.

It is preferable that one substrate of the above-mentioned first andsecond substrates is a thin film transistor (hereinafter, also referredto as “TFT”) array substrate having a TFT serving as a switching elementand a pixel electrode arranged in a matrix shape. It is also preferablethat the other substrate of the above-mentioned first and secondsubstrates is a color filter substrate (hereinafter, also referred to as“CF substrate”) having a color filter and a common electrode. Asmentioned above, the liquid crystal display device produced by theproduction method of the present invention is preferably an activematrix-type liquid crystal display device, but may be a simplematrix-type liquid crystal display device. If a simple matrix-typeliquid crystal display device is produced by the production method ofthe present invention, as the first substrate and the second substrate,a combination of a substrate provided with stripe-shaped signalelectrodes (column electrodes) and a substrate provided withstripe-shaped scanning electrodes (row electrodes) arranged so as to besubstantially perpendicular to the scanning electrodes may be mentioned.

A pixel is specified by the pixel electrode and the common electrodefacing the pixel electrodes in the active matrix-type liquid crystaldisplay device. In the simple matrix-type liquid crystal display device,a pixel is specified by the intersection of the strip-shaped signalelectrode and the scanning electrode.

The liquid crystal mode in the above-mentioned liquid crystal layer isnot especially limited, but Vertical Alignment (VA) mode in which domaindivision is provided is preferable. That is, it is preferable that theabove-mentioned liquid crystal layer contains liquid crystal moleculeswith negative dielectric anisotropy, and the above-mentioned firstalignment film and the above-mentioned second alignment film align theliquid crystal molecules substantially vertically the surfaces of thefirst alignment film and the second alignment film. The presentinvention utilizes the scanning exposure, and therefore is suitable forliquid crystal display devices in liquid crystal modes, such as VA modein which domain division is provided, in which the alignment film needto control the pretilt angle of the liquid crystal molecules with highaccuracy.

As the above-mentioned VA mode in which domain division is provided,VATN mode, VAECB mode, VAHAN mode and the like may be mentioned. Amongthem, VATN mode is most preferably used. That is, it is preferable inthe production method of the liquid crystal display device of thepresent invention that the exposure and attachment of the firstsubstrate and the second substrate are performed such that a directionof the scanning exposure for the first alignment film and a direction ofthe scanning exposure for the second alignment film are substantiallyperpendicular to each other. In VATN mode, both of the first alignmentfilm and the second alignment film have alignment patterns antiparallelto each other, which continue over a plurality of pixel regions.Therefore, use of the alignment treatment method according to thepresent invention permits easily formation of four domains inside thepixel region, whereby to provide an excellent viewing anglecharacteristic. In addition, it is especially important to perform thealignment treatment of the alignment film stably, because, in VATN mode,the pretilt angle of the liquid crystal molecules has a large influenceon display characteristics of the liquid crystal display.

In the present description, “the exposure and attachment of the firstsubstrate and the second substrate are performed such that a directionof the scanning exposure for the first alignment film and a direction ofthe scanning exposure for the second alignment film are substantiallyperpendicular to each other” means that the alignment direction of theliquid crystal molecules near the first alignment film and the alignmentdirection of the liquid crystal molecules near the second alignment filmare not necessarily perpendicular to each other completely as long asthe alignment directions are substantially perpendicular to each otherto provide liquid crystal display in VATN mode. More specifically, thealignment direction of the first alignment film and the alignmentdirection of the second alignment film preferably cross at 85 to 95degrees.

In the production method of the liquid crystal display device accordingto the present invention, the exposure and the attachment of thesubstrates are performed such that the direction of the scanningexposure in the first alignment film and the direction of the scanningexposure in the second alignment film facing the first alignment filmare substantially parallel to each other to produce a liquid crystaldisplay device in VAECB mode. In VAECB mode, however, the productionmethod according to the present invention can only produce a liquidcrystal display device having up to two domains in one pixel.

As the exposure device for alignment treatment used in the presentinvention, preferred is an exposure device for alignment treatmentcomprising: a stage; a light source for emitting a light beam at anincident angle of 0 degree or more and less than 90 degrees to thenormal line on the stage surface; and means for moving the stage and/orthe light source in antiparallel directions. The present inventioninclude such an exposure device for alignment treatment comprising astage and a light source, wherein the light source emits a light beam atan incident angle of 0 degree or more and less than 90 degrees to thenormal line on the stage surface, and the exposure device for alignmenttreatment further comprises means for moving the stage and/or the lightsource in antiparallel directions. Such an exposure device for alignmenttreatment according to the present invention provides photo-alignmenttreatment by the scanning exposure, and therefore the photo-alignmenttreatment can be performed more efficiently and stably as compared withthe photo-alignment treatment by the simultaneous exposure. Therefore,the exposure device for alignment treatment is most preferably used forthe alignment treatment of the liquid crystal display devices in VATNmode and the like.

The above-mentioned stage is not especially limited as long as thereonthe first substrate and/or the second substrate can be placed. A stagecapable of fixing the substrate by vacuum adsorption, and the like ispreferred. With respect to the light irradiation form of theabove-mentioned light source, a plurality of light sources is preferablydisposed at regular distances if the exposure is performed without aphotomask. If the exposure is performed through a photomask, thearrangement form of the above-mentioned light source is not especiallylimited. It is preferable that the light beam emitted to theabove-mentioned stage is converted into polarized light using apolarizer and the like. The above-mentioned exposure device foralignment treatment preferably includes a camera for image detection andan image processing device, which makes it possible to control thescanning direction while scanning the pattern on the substrate.

In the production method of the liquid crystal display device accordingto the present invention, the scanning exposure is performed whilescanning each pixel region more than one time in antiparalleldirections, and therefore, the alignment treatment can be providedefficiently and stably for the alignment film of the liquid crystaldisplay device, in which a plurality of domains are formed inside thepixel region. Such production method of the liquid crystal displaydevice according to the present invention is suitably applied toproduction of the liquid crystal display devices in VATN mode.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will, hereinafter, be described in more detailwith reference to Embodiments, but the present invention is not limitedto these Embodiments.

(Embodiment 1)

A production method of a liquid crystal display panel in 4VATN mode inEmbodiment 1 according to the present invention is mentioned below withreference to FIGS. 1( a) to 3. FIG. 1( a) is a plane view schematicallyshowing a light beam emitting direction to a photo-alignment film on aTFT array substrate in Embodiment 1. FIG. 1 (b) is a plane viewschematically showing a light beam emitting direction to aphoto-alignment film on a CF substrate in Embodiment 1. FIG. 2( a) is aplane view schematically showing the TFT array substrate as the firstsubstrate in Embodiment 1. FIG. 2( b) is a plane view schematicallyshowing the CF substrate as the second substrate in Embodiment 1. FIG. 3is a perspective view schematically showing an exposure device inEmbodiment 1.

First, a pair of the first substrate and the second substrate eachhaving no alignment film is prepared by a usual method. As the firstsubstrate, a TFT array substrate shown in FIG. 2( a), which is preparedas follows, is used. (1) the scanning signal line 15, (2) the TFT 11,(3) the pixel electrode 12 and (4) the data signal line 16 aresuccessively formed on a glass substrate (not shown) to dispose thescanning signal line 12 and the data signal line 16 in a matrix shape onthe substrate with an insulating film (not shown) therebetween, and theTFT 11 and the pixel electrode 12 are disposed at an intersection of thescanning signal line 15 and the data signal line 16. As the secondsubstrate, a CF substrate shown in FIG. 2 (b), which is prepared asfollows, is used. (1) the Black Matrix (BM) 13, (2) the color filter 14,(3) the protective film (not shown) and (4) the transparent electrodefilm (not shown) are successively formed on a glass substrate (notshown) to dispose the BM 13 on the substrate in a matrix shape, and thecolor filter 14 is disposed at a region partitionedby the BM 13. Thesubstrate is not especially limited to a glass substrate as long as ithas an insulating surface. Materials usually used may be used asmaterials for the above-mentioned components.

Then, a solution containing a photo-alignment film material is appliedto the TFT array substrate and the CF substrate by spin cast method andthe like, and calcined at 180° C. for 60 minutes to form a verticalphoto-alignment film on both substrates. The photo-alignment filmmaterial is not especially limited, and a resin containing aphotosensitive group, and the like may be mentioned. Specific preferredexamples of such a resin include polyimide containing a photosensitivegroup such as 4-chalcone group (the following chemical formula (1)), 4′-chalcone group (the following chemical formula (2)), coumarin group(the following chemical formula (3)), and cinnamoyl group (the followingchemical formula (4)). The above-mentioned photosensitive groups (1) to(4) generate crosslinking reaction (including dimerization reaction),isomerization, photo-realignment, and the like, by light beamirradiation. Use of the photo-alignment film material containing thephotosensitive group can more effectively reduce variation in thepretilt angle as compared with use of decomposition photo-alignment filmmaterials. The photosensitive groups in the following formulae (1) to(4) may have a structure in which a substituent group is bonded to thebenzene ring. A cinnamate group (C₆H₅—CH═CH—COO—), in which an oxygenatom is further bonded to the carbonyl group in the cinnamoyl grouprepresented by the formula (4), has an advantage of easy synthesis.Accordingly, polyimide containing a cinnamate group is more preferableas the photo-alignment film material. The calcination temperature,calcination time and thickness of the photo-alignment film are notespecially limited and may be appropriately determined.

Then, a method of scanning exposure for the TFT array substrate isexplained. First, an exposure device is explained with reference to FIG.3. The exposure device 20 a in Embodiment 1 includes, as shown in FIG.3, the stage 21 for placing the substrate 26 thereon, the light source22 having a lamp, a polarizer, and an optical filter, and the photomask23 mounted below the light source and in a light beam emittingdirection. The stage 21, and/or the light source 22 and the photomask 23are designed to be capable of moving relatively horizontally. Such aconfiguration enables the exposure device 20 a to perform scanningexposure for the photo-alignment film formed on the substrate surface bya light beam emitted through openings (not shown) formed in thephotomask 23. The light source 22 is designed to be capable of beinginclined toward the oblique direction to the stage 21 and the photomask23. As a result, the exposure device 20 a can perform scanning whileirradiating the photo-alignment film formed on the substrate surfacewith light from an appropriate oblique direction. The lamp is notespecially limited, and may be a low-pressure mercury lamp, a deuteriumlamp, a metal halide lamp, an argon resonance lamp, a xenon lamp, andthe like. Laser, such as excimer laser, may be used instead of the lamp.The wavelength of the emitted light maybe appropriately determineddepending on the alignment film material and the like, and ultravioletradiation is preferably used. The extinction ratio of the polarizer, thekind of the optical filter, the proximity gap that is a distance betweenthe substrate and the photomask, and the like, may be appropriatelydetermined.

Then, a method of exposing the TFT array substrate is explained withreference to FIG. 1( a). First, the TFT array substrate is placed on thestage of the exposure device. As shown in FIG. 1( a), a plurality ofopenings 24 a was formed inside the photomask 23 a. This opening 24 ahas a rectangular planar shape and has a width W1 which is substantiallyhalf the pixel pitch in the scanning signal line 15 direction(horizontal direction in FIG. 1( a)). The pitch of the plurality ofopenings 24 a is designed to have the same length as that of the pixelpitch in the scanning signal line 15 direction. Then, the end of theopening 24 a of the photomask 23 a is positioned along the data signalline 16. The scanning exposure is performed along the data signal line16 in the scanning direction −y (downward direction in FIG. 1 (a))continuously over a plurality of pixel regions from one end of the TFTarray substrate to the other. Then, the position of the opening 24 a ismoved horizontally by substantially half the width of the pixel pitch inthe scanning signal line 15 direction to similarly position the end ofthe opening 24 a along the data signal line 16. Then, the scanningexposure is similarly performed along the data signal line 16 in thescanning direction +y (in the direction antiparallel to the scanningdirection −y, that is, upward direction in FIG. 1( a)) from one end ofthe TFT array substrate to the other. As a result, one pixel region ofthe TFT array substrate is divided into two regions: region A and regionB, where the alignment directions are antiparallel. The scanningexposure is dramatically excellent in stability of the irradiance levelas compared with fractionated exposure and the like, and therefore caneffectively suppress variation in characteristics in each region A andB, such as the alignment direction, and the pretilt angle. The planarshape of the opening 24 a is not especially limited as long as a desireddomain pattern can be formed. Besides the planar shape, circular,ellipse, substantially linear shape (strip-shaped) and the like may bementioned. The width W1 of the opening 24 a may be appropriatelydetermined depending on a desired domain pattern, and it is preferablydetermined such that a non-irradiated region is not formed after thescanning exposure.

Then, a method of exposing the CF substrate is explained with referenceto FIG. 1 (b). First, the CF substrate is placed on the stage of theexposure device. As shown in FIG. 1 (b), a plurality of openings 24 bare formed inside the photomask 23 b formed. The opening 24 b has arectangular planar shape and has a width W2 which is substantially halfthe pixel pitch in the direction (upward and downward direction in FIG.1 (b)) of the BM 18 formed at the position corresponding to the datasignal line of the TFT array substrate (hereinafter, also referred to as“BM above data line”). The pitch of the plurality of openings 24 b isdesigned to have the same length as that of the pixel pitch in the BMabove data line 18 direction. Then, the end of the opening 24 b of thephotomask 23 b is positioned along the BM 17 formed at the positioncorresponding to the scanning signal line of the TFT array substrate(hereinafter, also referred to as “BM above scanning line”). Thescanning exposure is performed along the BM above scanning line 17 inthe scanning direction +x (rightward direction in FIG. 1 (b))continuously over a plurality of pixel regions from one end of the CFsubstrate to the other. Then, the position of the opening 24 b is movedhorizontally by substantially half the width of the pixel pitch in theBM above data line 18 direction to similarly position the end of theopening 24 b to the BM above scanning line 17. Then, the scanningexposure is similarly performed from one end of the CF substrate to theother along the BM above scanning line 17 in the scanning direction −x(in the direction antiparallel to the scanning direction +x, that is,leftward direction in FIG. 1 (b)). As a result, one pixel region of theCF substrate is divided into two regions: region C and region D, wherethe alignment directions are antiparallel. The scanning exposure caneffectively suppress variation in the characteristics in each region Cand D, as in the scanning exposure provided for the TFT array substrate.The planar shape of the opening 24 b is not especially limited as longas a desired domain pattern can be formed. Besides the planar shape,circular, ellipse, substantially linear shape (strip-shaped) and thelike may be mentioned. The width W2 of the opening 24 b may beappropriately determined depending on a desired domain pattern, and itis preferably determined such that a non-irradiated region is not formedafter the scanning exposure.

Embodiment 1 describes the method of the scanning exposure using thephotomask, but the photomask may not be used. In this case, it ispreferable that the light beam shape on the alignment film surface isappropriately adjusted with an optical lens and the like. It ispreferable that an incident angle of the emitted light beam to thenormal line on the substrate surface is 5 or more degrees and 70 or lessdegrees in order to provide the liquid crystal molecule with a pretiltangle suitable in 4VATN mode, although depending on the material for thealignment film to be exposed. It is also preferable that the irradiancelevel and the scanning speed at the scanning exposure are appropriatelydetermined. However, a light beam does not need to have an incidentangle, and the incident angle may be 0 degree, if appearance of thepretilt angle depends on the moving direction of the photo-irradiatedregion, as in the photo-alignment method disclosed in “Photo-RubbingMethod: A Single-Exposure Method to Stable Liquid-Crystal Pretilt Angleon Photo-Alignment Film”, M. Kimura, three et al, IDW′ 04: proceedingsof the 11th International Display Workshops, IDW′ 04 Publicationcommittee, 2004, and LCT2-1, p. 35-38. In 4VATNmode, the scanningdirection on the TFT array substrate and that on the CF substrate arenot especially limited to those shown in FIGS. 1 (a) and 1 (b) as longas the scanning directions on the substrates are substantiallyperpendicular to each other when the substrates are attached to eachother.

Then, plastic beads in 4 μm, for example, are spread over the TFT arraysubstrate or the CF substrate subjected to the scanning exposure, andthen the substrates are attached to each other. The relationship of thelight beam emitting directions in one pixel region of the bothsubstrates is as shown in FIG. 7. In each domain, the scanningdirections of the substrates facing each other are substantiallyperpendicular to each other.

Then, if a nematic liquid crystal material with negative dielectricanisotropy is injected between the substrates, the liquid crystalmolecules appear pretilt angles in directions different from one domainto another. As a result, in each domain, the alignment direction of theliquid crystal molecules near the center in the in-plane direction andthe thickness direction of the liquid crystal layer is inclined at 45degrees from the light beam emitting direction. Therefore, the liquidcrystal molecules in four domains incline in four different directionsrespectively when a signal voltage is applied to the produced liquidcrystal display panel. As a result, a wide viewing angle can beprovided. The pretilt angle is not especially limited, but it ispreferably 85 degrees or more and less than 90 degrees in 4VATN mode interms of increase in transmittance of the liquid crystal display panel.It is also preferable that the variation in the pretilt angle is within0.5 degrees in 4VATN.

Then, two polarizers are attached to each outside of the substrates suchthat each other's absorption axes are perpendicular and one of theabsorption axes is parallel to the bus line (the scanning signal line orthe data signal line) of the TFT array substrate. Thereby, the liquidcrystal molecules align substantially vertically at OFF-state, andtherefore the liquid crystal display panel can provide excellent blackdisplay (normally black mode). The liquid crystal display panel has fourdomains for aligning the liquid crystal molecules in four differentdirections, respectively, and therefore exhibits display characteristicshardly depending on a viewing angle direction. As mentioned above, theproduction method of the liquid crystal display panel in Embodiment 1adopts the scanning exposure. Therefore, a liquid crystal panel in 4VATNmode having domains with small variation in the characteristics can beproduced with a small number of alignment treatments.

(Embodiment 2)

A production method of a liquid crystal display panel in 4VATN mode inEmbodiment 2 according to the present invention is mentioned below withreference to FIG. 4. FIG. 4 is a perspective view schematically showingan exposure device in Embodiment 2. The liquid crystal display panel in4VATN mode in Embodiment 2 is produced in the same manner as inEmbodiment 1, except for the configuration of the exposure device andthe embodiment of the scanning exposure. Therefore, overlapping contentsbetween Embodiment 1 and Embodiment 2 are omitted.

First, the exposure device in Embodiment 2 is explained with referenceto FIG. 4. As shown in FIG. 4, the exposure device 20 b in Embodiment 2has a configuration in which the exposure device 20 a in Embodiment 1further comprises the camera for image detection 25 for detecting alinear micropattern, such as the bus line (the scanning signal line orthe data signal line) and the BM formed on the substrate. According tosuch a configuration, the exposure device 20 b in Embodiment 2 analyzesand processes images taken by the camera for image detection 25, wherebyto identify positions of the stage 21, and/or the photomask 23 and thelight source 22 based on the taken images.

Then, a method of the scanning exposure in Embodiment 2 is explained.First, the substrate 26, which is an object to be exposed, is placed onthe stage 21. Then, the stage 21, and/or the photomask 23, and lightsource 22 are automatically moved horizontally to an exposure startingposition, based on position data obtained by analysis and processes ofimages of the BM, the bus line and the like, formed on the substrate,the images being taken by the camera for image detection 25, and therebyto set an opening (not shown) of the photomask 23 to a predeterminedposition. Similarly during the light beam irradiation treatment, imagestaken by the camera for image detection 25 are analyzed and processedand then the scanning exposure is performed while correcting thepositions of the stage 21, and/or the photomask 23 and the light source22 point by point such that the position of the openings is not out ofalignment with the bus line, the BM, and the like. As mentioned above,the production method of the liquid crystal display panel in Embodiment2 uses the camera for image detection 25 to identify the exposurestarting position and correct the exposure position. Therefore, desireddomains can be formed inside the pixel region with high accuracy even ifthe TFT array substrate or the CF substrate has a distorted pixel array.

The present application claims priority under the Paris Convention andthe domestic law in the country to be entered into national phase onPatent Application No. 2005-350020 filed in Japan on Dec. 2nd, 2005, theentire contents of which are hereby incorporated by reference.

The terms “or more” and “or less” in the present description that thevalue described is included.

1. A production method of a liquid crystal display device comprising afirst substrate; a second substrate facing to the first substrate; aliquid crystal layer provided between the substrates; a first alignmentfilm provided on the liquid crystal layer side surface of the firstsubstrate; and a second alignment film provided on the liquid crystallayer side surface of the second substrate, wherein the productionmethod comprises subjecting the first alignment film and/or the secondalignment film to scanning exposure continuously over a plurality ofpixel regions, the scanning exposure comprises, in an inside of eachpixel region, a first scanning exposure for aligning liquid crystalmolecules in a first alignment direction and a second scanning exposurefor aligning liquid crystal molecules in a second alignment direction,the second alignment direction is parallel and opposed to the firstalignment direction, in the first scanning exposure and the secondscanning exposure, a light beam is made incident from an obliquedirection to a normal line on the substrate surface, and a light beamemitting direction of the first scanning exposure and a light beamemitting direction of the second scanning exposure are substantiallyantiparallel each other in the plan view of the substrate.
 2. Theproduction method of the liquid crystal display device according toclaim 1, wherein the liquid crystal layer contains liquid crystalmolecules with negative dielectric anisotropy, and the first alignmentfilm and the second alignment film align the liquid crystal moleculessubstantially vertically to the surfaces of the first alignment film andthe second alignment film.
 3. The production method according to claim2, wherein attachment of the first substrate and the second substrate isperformed such that a direction of the scanning exposure for the firstalignment film and a direction of the scanning exposure for the secondalignment film are substantially perpendicular to each other.
 4. Theproduction method according to claim 1, wherein the scanning exposure isperformed through a photomask between a light source and the firstalignment film and/or the second alignment film.
 5. The productionmethod according to claim 4, wherein the photomask is provided withopenings having substantially linear shape.
 6. The production methodaccording to claim 5, wherein a pitch between the openings in thephotomask has the same length as that of a pitch of the plurality ofpixel regions in a direction perpendicular to a direction of thescanning exposure.
 7. The production method according to claim 1,wherein the scanning exposure is continuously performed from one end ofthe first substrate and/or the second substrate to the other end of thefirst substrate and/or the second substrate.
 8. The production methodaccording to claim 1, wherein in the scanning exposure, an incidentangle of the light beam to the normal line on the substrate surface is 5or more degrees and 70 or less degrees.
 9. The production methodaccording to claim 1, wherein the light beam is polarized light.
 10. Theproduction method according to claim 1, wherein the light beam isultraviolet light.
 11. The production method according to claim 1,wherein pretilt angles of liquid crystal molecules are 85 or moredegrees and less than 90 degrees.
 12. The production method according toclaim 1, wherein a variation in the pretilt angles of the liquid crystalmolecules is within 0.5 degrees.
 13. The production method according toclaim 1, wherein a width of the plurality of regions subjected to thefirst scanning exposure or the second scanning exposure is substantiallyhalf pitch of the plurality of pixel regions in a directionperpendicular to a direction of the scanning exposure.
 14. Theproduction method according to claim 13, wherein area ratios of eachregion subjected to the first scanning exposure or the second scanningexposure in the each pixel are equal to each other.
 15. The productionmethod according to claim 1, wherein the liquid crystal display deviceincludes a first polarizer on the first substrate side and a secondpolarizer on the second substrate side, an alignment direction of thefirst alignment film is parallel to an absorption axis of the firstpolarizer, and an alignment direction of the second alignment film isparallel to an absorption axis of the second polarizer.
 16. Theproduction method according to claim 1, wherein the scanning exposure isperformed while correcting the position of the light beam based on dataof the position detected by a camera.
 17. The production methodaccording to claim 1, wherein each of scanning directions of the firstscanning exposure and the second scanning exposure is parallel to aborder of two regions in which alignment directions are parallel andopposed to each other.
 18. A liquid crystal display device of VATN modeproduced by using the production method of the liquid crystal displaydevice according to claim 1.